A power converter including a semiconductor module integrating a semiconductor device such as a switching element is used for a hybrid car or electric automobile. This power converter includes a cooler for cooling the heat-generating semiconductor module. There is a cooler described in, for example, Patent Document 1 as the cooler employed for the power converter.
The cooler in Patent Document 1 includes a cooling pipe having a refrigerant passage through which refrigerant circulates, and an inner fin disposed in the refrigerant passage. A plate material made of metal is pressed to form the inner fin, and the inner fin includes partition walls. Arranging the inner fin in the refrigerant passage forms fine passages obtained by dividing the refrigerant passage into several passages.